The true story behind Grace Kelly's two Cartier engagement rings

Grace Kelly's mammoth 10.48-carat Cartier ring has long been regarded as one of the most iconic royal and celebrity engagement rings of all time.

Yet it's more than just a pretty piece of jewellery; it has an intriguing story behind it, and wasn't the only engagement ring Grace received from Prince Rainer III of Monaco.

After the couple's romance began in 1955, when they met at the Cannes Film Festival, the Monegasque royal proposed to Grace with an altogether different ring.

In January 1956, the Hollywood star showed off a Cartier eternity band set with rubies and diamonds during a press conference at her parents' Philadelphia home.

The stones were reportedly taken from heirlooms from the Monegasque royal family and chosen by Rainier because their colours – red rubies and white diamonds – matched the national flag of Monaco.

Grace seemed smitten with the ring when she was seen in it in early 1956, but by the time she and Rainier wed, she had a different ring adorning her left hand.

And boy, was this one bigger.

The ring that has since gone down in history was a 10.48-carat diamond ring, also made by Cartier, that featured a huge emerald-cut centre stone flanked by two baguette-cut side stones.

The design was simple, but it was still a show-stopper for its sheer size alone, not to mention the fact it was worn by one of the most famous actresses of the 1950s.

It even made its movie debut in Grace's last on-screen appearance in 1956's High Society, with rumours it was actually created for her to wear in the film.

Grace starred as a wealthy socialite with three love interests, including a fiancé. Her character had to wear an engagement ring and she chose to wear her own in the scenes.

At one point in the movie, another character remarks on the size of the diamond, while in another Grace herself polishes the ring and admires it.

Naturally, fans went wild over the ring when it appeared on screen.

According to some rumours, Rainier actually gave her the incredible ring specifically to wear in High Society, as Grace was originally meant to wear a large prop ring.

As the theory goes, he bought the ring so she could wear a real diamond in the film and Grace continued to wear it as her real engagement ring after the fact.

But the rumour has never been confirmed, and other royal experts believe it was always meant to be her engagement ring, suggesting Rainier gave her the first eternity band as a placeholder while the huge 10.48 carat diamond was sourced.

Though both Cartier rings were worn by the royal until her untimely death in 1982, it was her huge diamond ring that now lives on as one of her most iconic pieces of jewellery.

Grace is believed to have been a long-time fan of Cartier, having reportedly been introduced to the jewellery house by film director Alfred Hitchcock.

Her impact on the brand can't be understated – just like her iconic ring - and to this day, an entire room of Cartier's New York boutique is dedicated to her.

However, they didn't get her rings; the diamond ring was loaned to the boutique when it first opened the Princess Grace room, but has since been replaced by a replica.

The real rings both now remain in the collection of the House of Grimaldi.